Cutting tool for cleaning out the femur medullary space and artificial hip to be inserted into this space

ABSTRACT

Milling tool for emptying the femoral medullary space, while creating a space for the shaft of a hip prosthesis, which comprises a flexible core ( 10 ) and a plurality of conical, rotationally symmetrical milling segments ( 12 ), mounted in superimposed manner on the core ( 10 ) and provided with a central through-bore, the milling segments ( 12 ) being so connected to the core ( 10 ) and/or the milling segments ( 12 ) adjacent thereto, that a rotational force applied to the core ( 10 ) and/or the upper segment ( 12 ) is transferred to the individual milling segments ( 12 ), as well as a hip prosthesis with a conically directed shaft and a ball ( 16 ) mounted on the proximal end of the shaft and which comprises a flexible core ( 10 ), a plurality of conical, rotationally symmetrical segments ( 12 ), mounted in superimposed manner on the core ( 10 ) and provided with a central through-bore and a device ( 14 ) for tensioning the core ( 10 ) to bring about a stiffening of the shaft formed from the individual segments ( 12 ).

The invention relates to a milling tool for emptying the femoral medullary space, whilst creating a space for the shaft or shank of a hip prosthesis and a hip prosthesis suitable for insertion in said space.

The insertion of a hip prosthesis comprising a shaft and a ball to be attached at an angle thereto is a frequent, regularly relatively uncomplicated surgical operation.

However, difficulties arise in those cases in which the femoral medullary space to be emptied with the aid of a milling tool prior to the insertion of the hip prosthesis shaft is not straight, but instead curved, because then when using the conventional, straight milling tools regularly and in undesired manner bony substance to be maintained is also milled off.

DE 29 14 455 discloses a device for producing a cavity in a bone for the insertion of an artificial joint part, in which two rasp halves adapted to the shape of the bone cavity to be produced are placed on a flexible turning tool drive shaft, the two rasp halves being movable against one another in the axial direction.

WO 94/27507 discloses a milling tool for emptying the femoral medullary space, whilst creating a space for the shaft of a hip prosthesis, having a flexible core and a plurality of conical, rotationally symmetrical milling segments, mounted in superimposed manner on the core and provided with central through-bores, which transfer or transmit a rotational force applied to the core. The pins provided therein for transferring the rotational force shear off, however, on bending the core in non-straight femoral medullary spaces.

The problem of the invention is to provide a milling tool making it possible to create a space for a hip prosthesis shaft following the path of the femoral medullary space, as well as a hip prosthesis, which can be inserted in such a non-straight, emptied femoral medullary space.

According to the invention this problem is solved by the features of claims 1 and 7. The subclaims relate to preferred developments of the invention.

The invention is described in greater detail hereinafter relative to the drawings, wherein show:

FIG. 1 A diagrammatic representation of such a milling tool in an untensioned core.

FIG. 2 A representation corresponding to FIG. 1 for a tensioned core.

FIG. 3 The hip prosthesis with an untensioned core.

FIG. 4 A representation corresponding to FIG. 3 for a tensioned core.

The milling tool shown in FIGS. 1 and 2 comprises a flexible core and a plurality of conical, rotationally symmetrical milling segments provided with a not shown, central through-bore and mounted in superimposed manner on the core 10.

The core is cross-sectionally noncircular and the through-bore of the milling segments 12 is provided with a correspondingly noncircular, axially directed through-bore (additively or alternatively the end faces of the individual milling segments 12 pointing towards one another can also be provided with meshing radial serrations). The central through bores have wasp waist cross-sections.

The core is provided with a tensioning device 14 acting on the upper milling segment 12 and whose tightening tensions the core 10 against the upper milling segment 12 and consequently brings about a mutual stiffening of the milling segments 12 (and consequently the shaft formed from the individual milling segments 12).

The drawing also shows that the end faces of the milling segments pointing towards one another are slightly convex, so that they can roll on one another.

The lowermost milling segment 12 is firmly attached to the core 10.

For emptying the femoral medullary space the milling tool is attached in the conventional manner with the core 10 untensioned. The distal milling segment 12 (the tip firmly connected to the core 10) will follow the path of the relatively soft femoral medullary space and the following milling segments follow this path. During the rotation of the milling tool resulting from the application of a rotational force to the core and/or the upper milling segment, they mainly only empty the soft material of the femoral medullary space, thereby protecting the bone. Thus, the milling tool “meanders” through the curved femoral medullary space and empties the same whilst protecting the bone material.

The hip prosthesis shown in FIGS. 3 and 4 has a corresponding construction. It comprises a flexible core 10, a plurality of conical, rotationally symmetrical segments, mounted in superimposed manner on the core 10 and provided with a central through-bore and a device 14 for tensioning the core 10 bringing about the stiffening of the shaft formed from the individual segments 12.

In the state shown in FIG. 3 in which the core 10 is not tensioned, the hip prosthesis shaft is driven into the previously emptied (not strictly linearly directed) femoral medullary space. During this process the individual segments 12 are so oriented (i.e. tilt with respect to the imaginary shaft axis), that the shaft is adapted to the femoral medullary space.

Following the driving in of the shaft the shaft core 10 is tensioned, so that the shaft is stiffened and loaded in the direction of an increasing straightening, which, due to the elasticity of the bone material, leads to a large-area engagement of the segments forming the shaft on the retained bony substance and consequently permits a much greater force transfer of the prosthesis shaft to the femur than would be possible when using a straight shaft. 

What is claimed is:
 1. A milling tool for emptying a femoral medullary space to form a space for a shaft of a hip prosthesis, comprising: a flexible core (10), a plurality of conical, rotationally symmetrical milling segments (12) mounted in superimposed manner on said flexible core (10) and having central through-bores, which transmit a rotational force applied to said core (10), and a tensioning device (14) that tensions said core (10).
 2. The milling tool according to claim 1, wherein said core (10) is cross-sectionally noncircular, and said plurality of milling segments (12) have correspondingly noncircular, axially directed through-bores.
 3. The milling tool according to claim 1, wherein said central through-bores have wasp waist cross-section.
 4. The milling tool according to claim 1, wherein said milling segments (12) have end faces with radial serrations.
 5. The milling tool according to claim 1, wherein said milling segments have slightly convex end faces.
 6. The milling tool according to claim 1, wherein said milling segments include a distally positioned milling segment (12) firmly attached to said core (10). 